On 27/05/20 14:11, Benjamin GAIGNARD wrote: > On 5/27/20 2:14 PM, Valentin Schneider wrote: >> On 27/05/20 12:17, Benjamin GAIGNARD wrote: >>> On 5/27/20 12:09 PM, Valentin Schneider wrote: >>>> Hi Benjamin, >>>> >>>> On 26/05/20 16:16, Benjamin Gaignard wrote: >>>>> A first round [1] of discussions and suggestions have already be done on >>>>> this series but without found a solution to the problem. I resend it to >>>>> progress on this topic. >>>>> >>>> Apologies for sleeping on that previous thread. >>>> >>>> So what had been suggested over there was to use uclamp to boost the >>>> frequency of the handling thread; however if you use threaded IRQs you >>>> get RT threads, which already get the max frequency by default (at least >>>> with schedutil). >>>> >>>> Does that not work for you, and if so, why? >>> That doesn't work because almost everything is done by the hardware blocks >>> without charge the CPU so the thread isn't running. >> I'm not sure I follow; the frequency of the CPU doesn't matter while >> your hardware blocks are spinning, right? AIUI what matters is running >> your interrupt handler / action at max freq, which you get if you use >> threaded IRQs and schedutil. > Yes but not limited to schedutil. > Given the latency needed to change of frequencies I think it could > already too late > to change the CPU frequency when handling the threaded interrupt. Right, on my Juno the transition latency (i.e. worse case) is about 1.2ms; I can see that eating into your time budget, depending on the framerate you're going for. Vincent's got a point, if you can limit that max-freq-hold to a single frequency domain, that would probably be a tad better. Thanks for persisting through my questioning :-) >> >> I think it would help if you could clarify which tasks / parts of your >> pipeline you need running at high frequencies. The point is that setting >> a QoS request affects all tasks, whereas we could be smarter and only >> boost the required tasks. > What make us drop frames is that the threaded IRQ is scheduled too late. > The not thread part of the interrupt handler where we clear the > interrupt flags > is going fine but the thread part not. >> >>> I have done the >>> tests with schedutil >>> and ondemand scheduler (which is the one I'm targeting). I have no >>> issues when using >>> performance scheduler because it always keep the highest frequencies. >>> >>> >>>>> When start streaming from the sensor the CPU load could remain very low >>>>> because almost all the capture pipeline is done in hardware (i.e. without >>>>> using the CPU) and let believe to cpufreq governor that it could use lower >>>>> frequencies. If the governor decides to use a too low frequency that >>>>> becomes a problem when we need to acknowledge the interrupt during the >>>>> blanking time. >>>>> The delay to ack the interrupt and perform all the other actions before >>>>> the next frame is very short and doesn't allow to the cpufreq governor to >>>>> provide the required burst of power. That led to drop the half of the frames. >>>>> >>>>> To avoid this problem, DCMI driver informs the cpufreq governors by adding >>>>> a cpufreq minimum load QoS resquest. >>>>> >>>>> Benjamin >>>>> >>>>> [1] https://lkml.org/lkml/2020/4/24/360 >>>>> >>>>> Benjamin Gaignard (3): >>>>> PM: QoS: Introduce cpufreq minimum load QoS >>>>> cpufreq: governor: Use minimum load QoS >>>>> media: stm32-dcmi: Inform cpufreq governors about cpu load needs >>>>> >>>>> drivers/cpufreq/cpufreq_governor.c | 5 + >>>>> drivers/media/platform/stm32/stm32-dcmi.c | 8 ++ >>>>> include/linux/pm_qos.h | 12 ++ >>>>> kernel/power/qos.c | 213 ++++++++++++++++++++++++++++++ >>>>> 4 files changed, 238 insertions(+)
